The driving dutchman

Hi all my 2001 F (abbingdon 1.8 mpi mk2) is every year hard to get through MOT emission tests.
Testing it with warm engine and adding Injection Cleaner takes is just below CO threshold.

To that I get regularely this warning: P0420 Catalyst System Efficiency Below threshold.


Usual suspect is the o2 sensor... attached some graphs of Torque where it looks like o2 sensors do seem to work....
If not good which one will needs to be replaced? Or has my CAT maybe died?



Please help me debugging and advise me on where to start fixing this.
Thanks in advance!